An estimated 200 million people still using Microsoft's mothballed operating system Windows XP are at risk of cyberattack, experts warned.
The U.S. technology giant stopped support for XP in April, meaning users will not get critical security updates, leaving the OS open to hacking and attack.
Research firm IDC outlined the large number of consumers and businesses under threat, showing that 200 million users are still on XP, while the OS has 26.2 percent market share, according to Netmarketshare numbers.
"You're talking about 200 million computers running XP, simply put, they are open," Ernest Hilbert, former FBI agent and head of cyber investigations for EMEA at risk consultancy Kroll, told CNBC in a phone interview.
Heartbleed, IE threat
This comes amid a series of cybersecurity concerns over the past few weeks. The so-called "Heartbleed bug" was discovered by researchers last month in OpenSSL software—an encryption service used by around two-thirds of websites to protect information sent to and from web pages.